Cook the pasta according to package instructions until al dente.
Heat olive oil in a pan over medium heat.
Add chopped onion and sauté until translucent.
Stir in minced garlic and cook for an additional minute.
Add the pumpkin puree and heavy cream to the pan, mixing well.
Season with nutmeg, salt, and pepper to taste.
Let the sauce simmer for about 5-7 minutes.
Drain the pasta and reserve some pasta water.
Combine the pasta with the pumpkin sauce, adding reserved water if needed.
Serve hot, garnished with fresh sage leaves and pumpkin seeds.